Use monkeypatch (python-pillow#9406)

Co-authored-by: Andrew Murray <radarhere@users.noreply.github.com>

Author: radarhere

Tests/test_file_pcx.py

@@ -119,36 +119,36 @@ def test_large_count(tmp_path: Path) -> None:
     _roundtrip(tmp_path, im)
 
 
-def _test_buffer_overflow(tmp_path: Path, im: Image.Image, size: int = 1024) -> None:
-    _last = ImageFile.MAXBLOCK
-    ImageFile.MAXBLOCK = size
-    try:
-        _roundtrip(tmp_path, im)
-    finally:
-        ImageFile.MAXBLOCK = _last
+def _test_buffer_overflow(
+    tmp_path: Path, im: Image.Image, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    monkeypatch.setattr(ImageFile, "MAXBLOCK", 1024)
+    _roundtrip(tmp_path, im)
 
 
-def test_break_in_count_overflow(tmp_path: Path) -> None:
+def test_break_in_count_overflow(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
     im = Image.new("L", (256, 5))
     px = im.load()
     assert px is not None
     for y in range(4):
         for x in range(256):
             px[x, y] = x % 128
-    _test_buffer_overflow(tmp_path, im)
+    _test_buffer_overflow(tmp_path, im, monkeypatch)
 
 
-def test_break_one_in_loop(tmp_path: Path) -> None:
+def test_break_one_in_loop(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> None:
     im = Image.new("L", (256, 5))
     px = im.load()
     assert px is not None
     for y in range(5):
         for x in range(256):
             px[x, y] = x % 128
-    _test_buffer_overflow(tmp_path, im)
+    _test_buffer_overflow(tmp_path, im, monkeypatch)
 
 
-def test_break_many_in_loop(tmp_path: Path) -> None:
+def test_break_many_in_loop(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> None:
     im = Image.new("L", (256, 5))
     px = im.load()
     assert px is not None
@@ -157,21 +157,21 @@ def test_break_many_in_loop(tmp_path: Path) -> None:
             px[x, y] = x % 128
     for x in range(8):
         px[x, 4] = 16
-    _test_buffer_overflow(tmp_path, im)
+    _test_buffer_overflow(tmp_path, im, monkeypatch)
 
 
-def test_break_one_at_end(tmp_path: Path) -> None:
+def test_break_one_at_end(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> None:
     im = Image.new("L", (256, 5))
     px = im.load()
     assert px is not None
     for y in range(5):
         for x in range(256):
             px[x, y] = x % 128
     px[0, 3] = 128 + 64
-    _test_buffer_overflow(tmp_path, im)
+    _test_buffer_overflow(tmp_path, im, monkeypatch)
 
 
-def test_break_many_at_end(tmp_path: Path) -> None:
+def test_break_many_at_end(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> None:
     im = Image.new("L", (256, 5))
     px = im.load()
     assert px is not None
@@ -181,10 +181,10 @@ def test_break_many_at_end(tmp_path: Path) -> None:
     for x in range(4):
         px[x * 2, 3] = 128 + 64
         px[x + 256 - 4, 3] = 0
-    _test_buffer_overflow(tmp_path, im)
+    _test_buffer_overflow(tmp_path, im, monkeypatch)
 
 
-def test_break_padding(tmp_path: Path) -> None:
+def test_break_padding(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> None:
     im = Image.new("L", (257, 5))
     px = im.load()
     assert px is not None
@@ -193,4 +193,4 @@ def test_break_padding(tmp_path: Path) -> None:
             px[x, y] = x % 128
     for x in range(5):
         px[x, 3] = 0
-    _test_buffer_overflow(tmp_path, im)
+    _test_buffer_overflow(tmp_path, im, monkeypatch)

Tests/test_file_png.py

@@ -654,21 +654,17 @@ def test_unknown_compression_method(self) -> None:
         with pytest.raises(SyntaxError, match="Unknown compression method"):
             PngImagePlugin.PngImageFile("Tests/images/unknown_compression_method.png")
 
-    def test_padded_idat(self) -> None:
+    def test_padded_idat(self, monkeypatch: pytest.MonkeyPatch) -> None:
         # This image has been manually hexedited
         # so that the IDAT chunk has padding at the end
         # Set MAXBLOCK to the length of the actual data
         # so that the decoder finishes reading before the chunk ends
-        MAXBLOCK = ImageFile.MAXBLOCK
-        ImageFile.MAXBLOCK = 45
-        ImageFile.LOAD_TRUNCATED_IMAGES = True
+        monkeypatch.setattr(ImageFile, "MAXBLOCK", 45)
+        monkeypatch.setattr(ImageFile, "LOAD_TRUNCATED_IMAGES", True)
 
         with Image.open("Tests/images/padded_idat.png") as im:
             im.load()
 
-            ImageFile.MAXBLOCK = MAXBLOCK
-            ImageFile.LOAD_TRUNCATED_IMAGES = False
-
             assert_image_equal_tofile(im, "Tests/images/bw_gradient.png")
 
     @pytest.mark.parametrize(

Tests/test_font_leaks.py

@@ -1,17 +1,15 @@
 from __future__ import annotations
 
+import pytest
+
 from PIL import Image, ImageDraw, ImageFont, _util
 
 from .helper import PillowLeakTestCase, features, skip_unless_feature
 
 original_core = ImageFont.core
 
 
-class TestTTypeFontLeak(PillowLeakTestCase):
-    # fails at iteration 3 in main
-    iterations = 10
-    mem_limit = 4096  # k
-
+class TestFontLeak(PillowLeakTestCase):
     def _test_font(self, font: ImageFont.FreeTypeFont | ImageFont.ImageFont) -> None:
         im = Image.new("RGB", (255, 255), "white")
         draw = ImageDraw.ImageDraw(im)
@@ -21,23 +19,29 @@ def _test_font(self, font: ImageFont.FreeTypeFont | ImageFont.ImageFont) -> None
             )
         )
 
+
+class TestTTypeFontLeak(TestFontLeak):
+    # fails at iteration 3 in main
+    iterations = 10
+    mem_limit = 4096  # k
+
     @skip_unless_feature("freetype2")
     def test_leak(self) -> None:
         ttype = ImageFont.truetype("Tests/fonts/FreeMono.ttf", 20)
         self._test_font(ttype)
 
 
-class TestDefaultFontLeak(TestTTypeFontLeak):
+class TestDefaultFontLeak(TestFontLeak):
     # fails at iteration 37 in main
     iterations = 100
     mem_limit = 1024  # k
 
-    def test_leak(self) -> None:
+    def test_leak(self, monkeypatch: pytest.MonkeyPatch) -> None:
         if features.check_module("freetype2"):
-            ImageFont.core = _util.DeferredError(ImportError("Disabled for testing"))
-        try:
-            default_font = ImageFont.load_default()
-        finally:
-            ImageFont.core = original_core
-
+            monkeypatch.setattr(
+                ImageFont,
+                "core",
+                _util.DeferredError(ImportError("Disabled for testing")),
+            )
+        default_font = ImageFont.load_default()
         self._test_font(default_font)

Tests/test_image.py

@@ -456,9 +456,11 @@ def test_register_open_duplicates(self) -> None:
         # Assert
         assert len(Image.ID) == id_length
 
-    def test_registered_extensions_uninitialized(self) -> None:
+    def test_registered_extensions_uninitialized(
+        self, monkeypatch: pytest.MonkeyPatch
+    ) -> None:
         # Arrange
-        Image._initialized = 0
+        monkeypatch.setattr(Image, "_initialized", 0)
 
         # Act
         Image.registered_extensions()

Tests/test_imagedraw.py

@@ -1485,21 +1485,15 @@ def test_stroke_multiline() -> None:
 
 
 @skip_unless_feature("freetype2")
-def test_setting_default_font() -> None:
-    # Arrange
+def test_setting_default_font(monkeypatch: pytest.MonkeyPatch) -> None:
     im = Image.new("RGB", (100, 250))
     draw = ImageDraw.Draw(im)
-    font = ImageFont.truetype("Tests/fonts/FreeMono.ttf", 120)
-
-    # Act
-    ImageDraw.ImageDraw.font = font
+    assert isinstance(draw.getfont(), ImageFont.load_default().__class__)
 
-    # Assert
-    try:
-        assert draw.getfont() == font
-    finally:
-        ImageDraw.ImageDraw.font = None
-        assert isinstance(draw.getfont(), ImageFont.load_default().__class__)
+    draw = ImageDraw.Draw(im)
+    font = ImageFont.truetype("Tests/fonts/FreeMono.ttf", 120)
+    monkeypatch.setattr(ImageDraw.ImageDraw, "font", font)
+    assert draw.getfont() == font
 
 
 def test_default_font_size() -> None:

Tests/test_imagefile.py

@@ -31,7 +31,7 @@
 
 
 class TestImageFile:
-    def test_parser(self) -> None:
+    def test_parser(self, monkeypatch: pytest.MonkeyPatch) -> None:
         def roundtrip(format: str) -> tuple[Image.Image, Image.Image]:
             im = hopper("L").resize((1000, 1000), Image.Resampling.NEAREST)
             if format in ("MSP", "XBM"):
@@ -55,12 +55,9 @@ def roundtrip(format: str) -> tuple[Image.Image, Image.Image]:
         assert_image_equal(*roundtrip("IM"))
         assert_image_equal(*roundtrip("MSP"))
         if features.check("zlib"):
-            try:
-                # force multiple blocks in PNG driver
-                ImageFile.MAXBLOCK = 8192
-                assert_image_equal(*roundtrip("PNG"))
-            finally:
-                ImageFile.MAXBLOCK = MAXBLOCK
+            # force multiple blocks in PNG driver
+            monkeypatch.setattr(ImageFile, "MAXBLOCK", 8192)
+            assert_image_equal(*roundtrip("PNG"))
         assert_image_equal(*roundtrip("PPM"))
         assert_image_equal(*roundtrip("TIFF"))
         assert_image_equal(*roundtrip("XBM"))
@@ -120,14 +117,11 @@ def test_incremental_webp(self) -> None:
             assert (128, 128) == p.image.size
 
     @skip_unless_feature("zlib")
-    def test_safeblock(self) -> None:
+    def test_safeblock(self, monkeypatch: pytest.MonkeyPatch) -> None:
         im1 = hopper()
 
-        try:
-            ImageFile.SAFEBLOCK = 1
-            im2 = fromstring(tostring(im1, "PNG"))
-        finally:
-            ImageFile.SAFEBLOCK = SAFEBLOCK
+        monkeypatch.setattr(ImageFile, "SAFEBLOCK", 1)
+        im2 = fromstring(tostring(im1, "PNG"))
 
         assert_image_equal(im1, im2)
 

Tests/test_imagefontpil.py

@@ -38,20 +38,18 @@ def test_invalid_mode() -> None:
             font._load_pilfont_data(fp, im)
 
 
-def test_without_freetype() -> None:
-    original_core = ImageFont.core
+def test_without_freetype(monkeypatch: pytest.MonkeyPatch) -> None:
     if features.check_module("freetype2"):
-        ImageFont.core = _util.DeferredError(ImportError("Disabled for testing"))
-    try:
-        with pytest.raises(ImportError):
-            ImageFont.truetype("Tests/fonts/FreeMono.ttf")
+        monkeypatch.setattr(
+            ImageFont, "core", _util.DeferredError(ImportError("Disabled for testing"))
+        )
+    with pytest.raises(ImportError):
+        ImageFont.truetype("Tests/fonts/FreeMono.ttf")
 
-        assert isinstance(ImageFont.load_default(), ImageFont.ImageFont)
+    assert isinstance(ImageFont.load_default(), ImageFont.ImageFont)
 
-        with pytest.raises(ImportError):
-            ImageFont.load_default(size=14)
-    finally:
-        ImageFont.core = original_core
+    with pytest.raises(ImportError):
+        ImageFont.load_default(size=14)
 
 
 @pytest.mark.parametrize("font", fonts)

Tests/test_psdraw.py

@@ -5,6 +5,8 @@
 from io import BytesIO
 from pathlib import Path
 
+import pytest
+
 from PIL import Image, PSDraw
 
 
@@ -47,21 +49,16 @@ def test_draw_postscript(tmp_path: Path) -> None:
     assert os.path.getsize(tempfile) > 0
 
 
-def test_stdout() -> None:
+def test_stdout(monkeypatch: pytest.MonkeyPatch) -> None:
     # Temporarily redirect stdout
-    old_stdout = sys.stdout
-
     class MyStdOut:
         buffer = BytesIO()
 
     mystdout = MyStdOut()
 
-    sys.stdout = mystdout
+    monkeypatch.setattr(sys, "stdout", mystdout)
 
     ps = PSDraw.PSDraw()
     _create_document(ps)
 
-    # Reset stdout
-    sys.stdout = old_stdout
-
     assert mystdout.buffer.getvalue() != b""